Wireless communication systems are widely deployed to provide various telecommunication services such as telephony, video, data, messaging, and broadcasts. Typical wireless communication systems may employ multiple-access technologies capable of supporting communication with multiple users by sharing available system resources (e.g., bandwidth, transmit power). Examples of such multiple-access technologies include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, single-carrier frequency division multiple access (SC-FDMA) systems, and time division synchronous code division multiple access (TD-SCDMA) systems.
These multiple access technologies have been adopted in various telecommunication standards to provide a common protocol that enables different wireless devices to communicate on a municipal, national, regional, and even global level. An example of a telecommunication standard is Long Term Evolution (LTE). LTE is a set of enhancements to the Universal Mobile Telecommunications System (UMTS) mobile standard promulgated by Third Generation Partnership Project (3GPP). It is designed to better support mobile broadband Internet access by improving spectral efficiency, lowering costs, improving services, making use of new spectrum, and better integrating with other open standards preferably using OFDMA on the downlink (DL), SC-FDMA on the uplink (UL), and may include using multiple-input multiple-output (MIMO) antenna technology.
Cooperative communications have been proposed to exploit diversity in order to achieve better network performance. The concepts for CoMP are proposed by 3GPP, e.g. in at least: Release 9, “Evolved Universal Terrestrial Radio Access (E-UTRA); Further advancements for E-UTRA physical layer aspects”; Release 11, “Coordinated Multi-Point Operation for LTE (CoMP)”; and Release 14, “Further Enhancements for Coordinated Multipoint (CoMP) joint transmission”, among others. 3GPP, Release 14 is considered as the commencement of the evolution of a 5G communications system.
CoMP transmission and reception actually refers to a wide range of techniques that enable dynamic coordination or transmission and reception with multiple geographically separated transmission points (TPs). Its aim is to achieve high data rates, improve the cell edge throughput and enhance the overall system performance. In the traditional cellular DL transmission, evidently the cell edges are the most challenging environment. Not only is the signal lower in strength because of the distance from the TP, but also interference levels from neighbouring TPs are likely to be higher as the UE will be closer to them.
CoMP therefore requires close coordination between a number of geographically separated TPs. They dynamically coordinate to provide joint scheduling and transmissions as well as providing joint processing of the received signals. In this way, a user equipment (UE) at the edge of a cell is able to be served by two or more TPs to improve signals reception/transmission and increase throughput particularly under cell edge conditions. Furthermore, the coordinated TPs can avoid scheduling the same frequency resource for the nearby UEs, which can avoid inter-cell interference (ICI).
There are three typical types of DL CoMP coordination mode discussed by 3GPP.
A first mode is Coordinated Scheduling (CS) where each UE is served by only one site. The site may be a macro/micro/pico cell, an evolved NodeB (eNB), a relay cell, a repeater, etc. The CS mode schedules the DL transmission from an eNB in a first cell to a UE in the same cell in different time-frequency resources than a transmission from an eNB in a neighbouring cell to a UE in said neighbouring cell so that any interference experienced by a UE in one cell from an eNB in a neighbouring cell is reduced.
A second mode is Coordinated Beamforming (CB). In this mode, the interference caused by an eNB in a first cell to a UE in a neighbouring cell can be reduced by spatially nulling the beams targeting said UE by certain coordination of the precoding between said eNB in the first cell and the eNB in the neighbouring cell. Interference caused by DL transmissions from the eNB in the neighbouring cell to a UE in the first cell can also be reduced by spatially nulling the beams targeting the UE in the first cell.
For both CS and CB, highly detailed feedback is required on the channel properties in a fast manner so that the changes can be made. Another requirement is for very close coordination between the TPs to facilitate the combination of data or fast switching of the cells.
The third mode is coherent joint transmission or joint processing. In this mode, multiple sites transmit the same signals at least over a subframe to the same UE simultaneously using the same resources. For example, an eNB in a first cell and an eNB in a second cell transmit the same signals to a UE in say the first cell using the same resource. The signals from the two eNBs are coherently combined in the air interface when they reach the UE. However, each serving site for the UE is required to allocate the same full set of resource blocks (RBs) to transmit the same subframe to the UE. If one site is to transmit a subframe of signal to a UE using a set of RBs, then another site cannot join the coherent joint transmission unless it has the same set of RBs available to transmit the same subframe. This requirement limits the time frequency resource utilization and restricts the scheduling and link adaptation.
This form of CoMP places a high demand on the backhaul network because the data to be transmitted to the UE needs to be sent to each eNB that will be transmitting it to the UE. This may easily double or triple the amount of data in the network dependent upon how many eNBs will be sending the data. In addition to this, joint processing data needs to be sent between all eNBs involved in the CoMP area.
US20160037511 discloses a method involving collecting channel state information (CSI) periodically reported by UEs served by a TP, e.g. eNB, within a cooperating set of eNBs in a serving CoMP-management agent (CoMP-MA). The CoMP-MA is a software entity running on or attached to each eNB participating in the CoMP transmission. The radio resource allocations, RLC and MAC headers, references to user plane data and precoding matrices are extracted from corresponding protocol entities and forwarded to transmitting network nodes in order that the transmitting CoMP-MA is able to prepare for air interface scheduling for the user terminal.
US20150098421 discloses a method involving configuring a first DL control channel for a UE being served by a first TP, such that the configuration facilitates decoding of the first DL control channel by a UE served by a second TP. The first DL control channel is transmitted. The first TP is a first base station and the second TP is a second base station. The first and second TPs share a same cell identifier (CID).
US2015189636 discloses a method involving allocating two sets of frequency resources for transmitting two sets of time slots of data in a subframe from communication nodes to a UE. One set of frequency resources is intersected with the other set of frequency resources. Union of the two sets of time slots of data is equal to the subframe. The latter set of frequency resources is selected from available frequency resources based on channel status information.
Despite technical challenges, joint transmission is one of the key improvements in 3GPP Release 14 in order to further enhance CoMP operation. In contrast to a CoMP system where a UE can be served by multiple coordinated TPs, DL transmissions for UEs at cell edges in a conventional cellular network system are typically scheduled on the same frequency resources and therefore the UEs will suffer strong ICI and high performance loss. With joint transmission as proposed in at least 3GPP Release 14, the coordination among TPs can avoid scheduling the same frequency resource for nearby UEs and avoid ICI.
In joint transmission, the coordinated TPs can have two coordination methods. The first method is to schedule the same frequency for a UE to improve spectral efficiency. The second one is to schedule different frequency resources to a UE to increase the transmission bandwidth. Both methods can improve the DL signal quality, especially for the cell-edge users. In addition, the overall system throughput will also be enhanced.
There is currently no resource allocation mechanism to indicate the joint transmission frequency resource allocation information to the UEs in the existing standard. Therefore, there is a need for a new resource allocation method and apparatus for resource allocation signaling in joint transmission systems.